Re: limited dynamic range of the BITX40

Jerry Gaffke
 

Reducing that front end RF gain could well help.
But Henning is suggesting that there's more than 15 or 20 dB at stake here:
  >  a dynamic range of 75 dB is possible, due to the audio preamp this range will be only 43.5 dB now!! We are loosing 31.5 dB of dynamic range!

I'm by no means an RF kind of guy.  
But I like his argument, and I like the idea of a PIN diode attenuator for AGC between the crystal filter and modulator.
That NXP BAP64Q quad PIN diode device is $0.25 in quantity, $0.50 for a single unit from Mouser.
With that AGC in place perhaps we can leave the first RF amp as is, so the rx still works with a poor antenna. 

Jerry


On Mon, Sep 4, 2017 at 01:12 pm, Ashhar Farhan wrote:
The bitx was sketched on a flight. I didnt know muchP about dynamic range. In retrospect, the rf amp severely compromises the dynamic range. Someone should measure the iip3 with and without the rf amp.
I thought of redoing the bitx design for Bitx40 but in the end, decided to stick to the original for it to be called a bitx.
It is a sum of many tradeoffs and lazy choices (like the LM386).
- f

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